One guy making a successful MMO? Sorry, can't be done.
Not only can it be done, it has been done. Like most other genres where people try to compete with multi-million dollar budgeted developers aiming at retail markets, it's those who are considerably more clever and come up with something cheaper, more practical and offering a different experience who are making the vast sums of money while those trying to remake WoW just waste an awful lot of their time and talents.